The effect of component partitioning on potassium picrate transport across multicomponent supported liquid membranes

Supported liquid membrane experiments were performed with systematically varied liquid membrane compositions including dicyclohexyl-18-crown-6 ether as the carrier and various ratios of methylene chloride and a 35 carbon aliphatic oil. The partitioning of the crown ether species toward the membrane phase increased markedly with methylene chloride addition to the aliphatic oil. p]The unanticipated unsteady state transport of potassium picrate across the liquidfilled microporous membranes resulted from evaporation of methylene chloride from the aqueous reservoirs and subsequent depletion from the membrane phase. The depletion of methylene chloride from the liquid membrane caused progressively reduced partitioning of the carrier and carrier complexes to the membrane relative to the contiguous aqueous phases. The reduction in carrier concentration in the membrane phase resulted in progressively decreased concentration gradients of the carrier complex. The rate of potassium picrate transport decreased during the course of the experiments even though the upstream potassium concentration was insignificantly decreased and the downstream concentration of potassium picrate remained small compared with the upstream concentration. p]These experimental results focus attention upon the important practical problem of non-infinite partitioning of carrier and key solvent components between the membrane phase and the contiguous aqueous phases. Subtle changes in the carrier distribution coefficient markedly compromise process efficacy since the volume ratio of the aqueous and membrane phases is enormous.